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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.security.acl;

import java.util.Enumeration;
import java.security.Principal;

/**
 * This interface is used to represent a group of principals. (A principal
 * represents an entity such as an individual user or a company). <p>
 *
 * Note that Group extends Principal. Thus, either a Principal or a Group can
 * be passed as an argument to methods containing a Principal parameter. For
 * example, you can add either a Principal or a Group to a Group object by
 * calling the object's {@code addMember} method, passing it the
 * Principal or Group.
 *
 * @author Satish Dharmaraj
 */
public interface Group extends Principal {

  /**
   * Adds the specified member to the group.
   *
   * @param user the principal to add to this group.
   * @return true if the member was successfully added, false if the principal was already a member.
   */
  public boolean addMember(Principal user);

  /**
   * Removes the specified member from the group.
   *
   * @param user the principal to remove from this group.
   * @return true if the principal was removed, or false if the principal was not a member.
   */
  public boolean removeMember(Principal user);

  /**
   * Returns true if the passed principal is a member of the group.
   * This method does a recursive search, so if a principal belongs to a
   * group which is a member of this group, true is returned.
   *
   * @param member the principal whose membership is to be checked.
   * @return true if the principal is a member of this group, false otherwise.
   */
  public boolean isMember(Principal member);


  /**
   * Returns an enumeration of the members in the group.
   * The returned objects can be instances of either Principal
   * or Group (which is a subclass of Principal).
   *
   * @return an enumeration of the group members.
   */
  public Enumeration<? extends Principal> members();

}
